How To Build a Self-Driving Mars Car—With Less Computing Power Than an iPhone

Type in the driving directions. Tap "enter." The code flies across the cosmos toward Mars. Minutes later, the signal arrives at the rover standing alert on the planet's surface. The plucky bot decodes the instructions to drive a meter or two that-a-way, in the direction of an interesting-looking rock. Agreeably, it rolls. And then the robot sits just there, as if thinking "now what?" as it waits for the next signal from home base.

This is no way to drive.

Slow going is a Martian way of life. Having invested years and billions of dollars to send a fragile rolling robot to another world, NASA isn't suddenly going to start doing donuts or drag-racing a dust storm. The rover is on its own—if something goes wrong, there's nary a mechanic in sight. And then there's the time lag: It takes 5 to 20 minutes to send directions one-way from Earth, depending upon the current distance to Mars. So NASA drives like a grandma. This spring, the Opportunity rover completed a the first Martian marathon. It took more than 11 years to drive those 26.2 miles.

Imagine an awesome future Mars car. It prowls instead of puttering, exploring vast swaths of the Red Planet. It's much more capable than any rover we've ever sent. And whether or not it's carrying humans, the Martian dream car probably drives itself.

On a basic level Mars rovers already have some limited autonomy, says NASA's Matt Heverly, who has guided both Curiosity and Opportunity. Curiosity can take a basic set of instructions and execute them on its own. But there are important reasons why we're still a long way from a badass Google car that bombs around Mars, cruising carefree as it explores the rocks, craters, and dunes.

How Mars Looks Through Curiosity's Eyes

Curiosity is actually on its own more than you might think. The reason is twofold. One is the time lag in sending the signals. It's a hell of lot less annoying to send a bunch of instructions at once than to drive with a minutes-long gap between call and response. The second reason is the way that Earth and Mars days are not quite in sync. The Martian day is 40 minutes longer than ours, meaning that to keep in sync with the rover's 9 to 5, NASA's people have to shift their daily schedules forward 40 minutes every day.

For the sake of employee sanity, Heverly and colleagues quit that after the first three months of Curiosity's mission. Now, they send it a list of instructions twice a day, and let the rover work its way through them while its human minders sleep or eat lunch. Here's how it works:

Curiosity sees the surface of Mars as if it's a scene from an Atari game. Even so, the rover has a pretty amazing ability to analyze the world around it—not by scanning the lines on a highway, but by understanding the unpredictable Martian terrain. When NASA can see all the rocks out in front of a rover, it can easily plot a course around them. But, Heverly says, the time comes when you've got to go over a hill and you don't know what's on the other side. So they trust the rover, essentially telling it: Go ahead, but keep yourself safe.

"If it can't figure out a path, it's the humans that are helping to get it to the next safe spot."

Heverly says Curiosity can take pictures at regular intervals of the ground in front of it and to its sides, building a 3D terrain mesh. The rover can then look at the map it has made, he says. "It can say, 'If I drove here, would there be a rock underneath my wheels and if so, how tall is that rock and is that safe for me?'"

Curiosity uses its map to evaluate possible paths, assigning them a sort of "safety score" and choosing the one most likely to keep it out of trouble. It takes a step in that direction and then evaluates its position again. There's a minimum score for these paths that Heverly calls the "goodness score," and if nothing satisfies the goodness scores, then nothing happens. "If it can't find a path," he says, "then it will stop and call home and just say, 'Hey, there doesn't appear to be anything out here in front of me that's safe enough.'"

You can only map the world so well with one-tenth the power of an iPhone, though. "We allow Curiosity to make a lot of decisions on its own and to drive autonomously. But if it can't figure out a path, it's really the humans that are helping to get it to the next safe spot where the computer can take over again."

A Light Bulb For an Engine

"The whole rover is powered off of 100 watts, which is basically one lightbulb in your house."

Curiosity creeps. It moves at just about 0.1 miles per hour to make sure it stays out of trouble. Here's an important part of the reason: While this roving machine cost $2.5 billion, it has about 10 times less computing power than the smartphone in your pocket.

Compare that meek power to what's available for terrestrial autonomous vehicles, the modern wonders set to dominate the auto industry and make human drivers obsolete. When Google builds a robot car, it builds a machine with the best computing technology available today. It uses a barrage of sensors all around the vehicle that allow the car to understand any driving situation it might find itself in, and to drive safely in traffic even with quickly changing environments and lots of moving hazards (read: humans at the wheel).

"That level of sophistication is kind of on the cutting edge here on Earth, but it's built on the same principles as what we're doing on Mars. They just have much more computational resources, they have many different sensors," Heverly says. "We're limited tremendously by weight and power because we can only land 900 kilograms safely on the surface of Mars and the whole rover is powered off of 100 watts, which is basically one lightbulb in your house. We run our entire rover on that."

ATHLETE

NASA

Why so limited? For one thing, spacecraft design is a long time coming. It takes years to go from the proposal page to the build—years in which the state of computing capability jumps forward another few generations. Then there's weight. NASA is obsessed with weight for a lot of reasons, starting with the fact that space launches get onerously more expensive the more pounds you add. Heverly is currently working on the Mars 2020 rover, which will be built on the same chassis and limited to the same size and weight as Curiosity. And there's energy. Curiosity is limited to the amount its radioisotope thermoelectric generator, which cooks up about 100 watts.

Hanging over all these design questions is simply the sheer difficulty of building electrical components that work, and won't fail, in hostile environments. "It has to survive a harsh radiation environment," Heverly says. "It has to survive the very cold temperatures. It has to be extremely reliable because we only get one chance. So we want to make sure that the computer works, and all those things together mean that we can't be as cutting-edge as consumer technology. We tend to use technology that is proven and robust because we just want to make sure that it works."

A True Martian Supercar

Mars cars could have it so much better. There's a point in the new film The Martian where Matt Damon's stranded astronaut starts zooming around in the nice ride that's part of the Ares III mission. It's like a hulking solar-powered space truck, one that has to carry him all around the planet as he tries to stay alive.

It's a pretty stellar rig. Andy Weir, author of the book version of The Martian, explained it to me this way:

"The Ares mission in the book—the way it worked was they just had this huge solar farm and about a 20-km range, so the rover could go out and come back and recharge. But if you actually wanted a completely self-contained system that could travel very long distances, then … I don't know. That's a fun thing to think about. I would go for extremely lightweight solar panels that unroll—something like that. You'd do your driving at night, and you'd camp during the day and just charge. Instead of Watney's makeshift system where he could only get about 2 or 3 hours of driving time with a charger, you'd get it so that it could drive 8 or 9 hours in a day."

Whether through souped-up solar or some kind of nuclear source like what Mark Watney rigs up in the book and movie, better energy tech could help to make Martian vehicles more rugged and capable. NASA's space-ready electronics and computing systems slowly will get better, too. Martian rovers and cars will get faster, driver further, and understand their surroundings much better. The question then becomes, what do you do with them?

"Can I go someplace and have it drive me there while I'm sleeping?"

In The Martian, Watney's ride is more like an overgrown version of the Apollo Lunar Rovers—a space car that humans drive from place to place. Heverly tells PM that he loved the book version of The Martian, but when he looks at an advanced rover capable of carrying humans on the Red Planet's surface, he thinks about what would be possible if such a thing could carry a much more advanced computer system than Curiosity's.

At today's NASA, the engineers and their rovers work together, with the humans taking over when things get rocky. "Humans are always good at getting vehicles out of unknown situations," he says. But when you're talking about a human-carrying Mars rover, the collaboration between man and machine could be just as important.

A few years ago, Heverly worked on NASA's concept for ATHLETE, the All-Terrain, Hex-Limbed, Extra-Terrestrial Explorer. With six legs that can transform into arms on demand, ATHLETE was meant to be a vision of a supercar for another world. It's a rolling habitat in which astronauts could reside, but could also because a ditch-digger that investigated the subsurface. Humans could drive it from inside, or NASA could remotely drive it from Earth. Or, Heverly says, "you could ask it to do its own thing while you're doing something else."

"Can I go someplace and have it drive me there while I'm sleeping, so that I can be awake in a new place to be aware and do my work when I'm there? Can I have a vehicle dig trenches for me or do some other sort of work while I'm taking measurements?" he says. "I think as we move into the future and as we envision humans moving to Mars, it can be less about transportation purely from point A to point B and more about cooperation."

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